The proposed research is aimed at: a) continuing our investigation on the behavior of utero-placental circqlation during experimentally-induced renal hypertension in the pregnant sheep. Severe form of hypertension will be produced by unilateral renal artery constriction and contralateral nephrectomy during the latter third of gestation. Since the data collected from animals with mild hypertension showed a different behavior from normotensive animals, we shall endeavor to investigate the mechanisms which make the utero-placental vascular bed behave differently in the normotensive and hypertensive condition; b) assessing the precise role of the renin-angiotensin-aldosterone system in te development of this type of hypertension, emphasis will be directed toward comparing renal and uterine output of renin before and after delivery; c) determining the role of the changes in the cardiac output and blood volume in the evolution of this type of hypertension and in the rebound in utero-placental circulation as pregnancy progresses; d) investigating the relation of the salt intake to this type of hypertension and to the changes in the renin-angiotensin system that occur during the hypertensive condition; e) attempting to assess the impact of this type of renal hypertension on the fetal circulation and metabolism at the same time the fetal plasma concentration of renin before and after the induction of hypertension will be compared to that of the mother; f) studying the effects of vasodepressor drugs, such as hydralazine, methyldopate and various adrenergic blocking agents on this type of hypertension and on the renin-angiotensin system; g) investigating whether the reactivity of the vascular system to angiotensin and other vasoactive substance is different in the hypertensive and normotensive condition.